Chapter 10.8, Problem 10.19P

Interpretation Introduction

Interpretation:

The function of the given reagent has to be identified.

Concept Introduction:

When a reagent functions as a nucleophile, substitution reaction takes place and when a reagent functions as a base, elimination reaction takes place.  The first step is to determine the reagent to be strong or weak nucleophile and whether it is a strong or weak base.  Basicity and nucleophilicity do not always parallel each other.

When comparing the atoms in the same row in periodic table, the basicity and nucleophilicity parallel each other.  An example is, ${\text{NH}}_{\text{2}}{}^{\text{-}}$ is stronger nucleophile than ${\text{OH}}^{\text{-}}$.

When comparing the atoms in the same column in periodic table, the basicity and nucleophilicity do not parallel each other.  An example is, ${\text{SH}}^{\text{-}}$ will be more stable than ${\text{OH}}^{\text{-}}$ and hence, ${\text{OH}}^{-}$ will be a stronger base.

Basicity measures the charge stability on atom, while nucleophlicity measures how fast a nucleophile attacks.  Basicity is a thermodynamic argument and nucleophilicity is a kinetic argument.

Nucleophile (Only):  This category consists of reagents that act only as strong nucleophiles and not as bases.  The reagent from this category involves in substitution reaction and not elimination.

Base (Only):  This category consists of reagents that act only as bases and not as nucleophiles.  The reagent from this category involves in elimination reaction and not substitution.

Strong Nucleophile/Strong Base:  This category consists of reagents that are strong bases and also strong nucleophiles.  This includes hydroxide, alkoxide ions.  Generally these reagents are used for bimolecular process.

Weak Nucleophile/Weak Base:  This category consists of reagents that are weak bases and weak nucleophile.  This includes reagents such as water, alcohols.  Generally these reagents are used for unimolecular process.